why should one prefer call_user_func_array over regular calling of function?

1. You have an array with the arguments for your function which is of indeterminate length.

   $args = someFuncWhichReturnsTheArgs();
   
   foobar( /* put these $args here, you do not know how many there are */ );
   

   The alternative would be:

   switch (count($args)) {
       case 1:
           foobar($args[0]);
           break;
       case 2:
           foobar($args[0], $args[1]);
           break;
       ...
   }
   

   Which is not a solution.

The use case for this may be rare, but when you come across it you need it.